US2576712A

US2576712A - Polymerization of liquid polymerizable organic compounds in elongated shapes

Info

Publication number: US2576712A
Application number: US113132A
Authority: US
Inventors: Boyko John
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1949-08-30
Filing date: 1949-08-30
Publication date: 1951-11-27
Anticipated expiration: 1968-11-27

Description

Nov. 27, 1951 J. BOYKO 2,576,712

POLYMERIZATION OF LIQUID POLYMERIZABLE ORGANIC COMPOUNDS IN ELONGATED SHAPES 7 Filed Aug. 50, 1949 INVENTOR.

JOHN BOYKO BY |8 ATTO NEY Patented Nov. 27, 1951 POLYMERIZATION OF LIQUID POLYMERIZ- ABLE ORGANIC COMPOUNDS IN ELON- GATED SHAPES John Boyko, Union, N. J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application August 30, 1949, Serial No. 113,132

This invention relates to a process of polymerizing liquid polymerizable organic compounds in elongated shapes and, more particularly, to a process of polymerizing methyl methacrylate in the form of rods.

Heretofore, various liquid polymerizable organic'compounds, particularly methyl methacrylate compositions, have been polymerized in the form of rods and other elongated shapes by the process disclosed in Fields U. S. Patent 2,057,674. In following this process, the apparatus disclosed in Fields U. S. Patent 2,238,443 has been used. This apparatus essentially consists of a plurality of elongated metal tubes, usually aluminum, vertically disposed in a container capable of confining a liquid. The process comprises introducing a heated liquid into the container and slowly raising the level of the liquid to polymerize the liquid polymerizable organic compound contained within the tubes at the level corresponding to the level of the heated liquid. The space above the heated liquid is maintained at a lower temperature to prevent premature polymerization' at levels above the heated liquid. Such a process of casting in metal tubes tends to give relatively low yields of satisfactory rods. In general, the rejected polymer rods contained voids owing to shrinkage of the polymer from rigid container Walls. Other difliculties include adhesion of the polymer to the metal walls thereby complicating removal of the polymer rod from the mold.

Another prior art method of producing polymer rods is to cast a liquid polymerizable organic compound in the form of a sheet in a cell composed of two sheets of glass separated by a compressible gasket, as disclosed in Rohm U. S. Patent 2,154,639. The polymeric sheet is cut into rods of square cross section, and cylindrical rods are cut by grinding on a lathe. In view of the amount of labor involved in preparing the cells for casting polymeric sheets, in addition to the amount of polymer Wasted in cutting and grinding, this process is not entirely satisfactory.

An object of the present invention is to provide a simplified, more'economical and highly eflicient method of producing polymeric materials in the form of elongated shapes. A more specific object is to provide a more simplified, economical and highly eflicient process for producing polymethyl methacrylate rods or elongated cylinders. Other objects will be apparent from the description of the invention given hereinafter.

The above objectsare accomplished according to the present invention by introducing a liquid polymerizable organic compound into a substantially vertically positioned. elongated cylindrical 6 Claims. (Cl. 1858) 0.010 inch thick and having a tensile strength equal to PDF wherein P is the maximum pressure, expressed in pounds per square inch, exerted by the polymerizable compound against the wall of the easing, D is the inside diameter, expressed in inches, of the casing, F is a factor ranging from 3.5 to 5, and T is the wall thickness of the casing expressed in inches, closing the upper end of the casing, and thereafter polymerizing the polymerizable compoundcontained in the casing while maintaining the casing in vertical position.

In a preferred form, the invention comprises using'methyl methacrylate as the liquid polymerizable organic compound and the casing used is from 12 to 72 inches long and has an inside diameter of 1 to 6 inches. It is still more preferred to use a casing which is 12 to 54 inches long and has an inside diameter of 1 to 2 inches.

The present invention resides in great part in the discovery that casings of synthetic linear polyamides within the wallithickness specified above and having a tensile strength equal to that specified, inherently-possessed the elasticity which permits such casingsto be used with a high degree of satisfaction in the polymerization of'liquid polymerizable organic compounds in the form of rods. The invention is applicable to any liquid polymerizable organic compound convertible to a solid upon polymerization and is particularly useful in the production of rods of polymethyl methacrylate. Ordinarily, the polymerizable compound will be polymerized by subjecting the filled casing 'to thermal energy although actinic energy may be used. After polymerization, the casing is stripped from the solid rod formed and the rod is then ground to give'a smooth flawless surface.

The invention will be further described with reference to the accompanying drawing wherein:

Fig. I is a horizontal section through an apparatus-adapted for carrying out the present invention;

Fig. 11 is a vertical section through the apparatus, shown in Fig. I;

Fig. III is a section, at right angles to the major axis, of a polymer rod before removal of the'polyamide casing; and Fig. IV is a section through the same rod after stripping the casing and grinding to remove surface imperfections. 1

Referring toFigs. I and II, reference numeral l designates a simple circulating air oven protom, the bottom ones only being illustrated. The? ring 8 carries a plurality of feet. l8 on.which the rack rests. i

The metal rack is designedt'o hold'a plurality of filled casings H between the inner concentric rings and 9. In carryingout the processcthe casings II are tied at thein'lower'en'ds lz-gfilled with the polymerizable liquid l3, and then-tied at the upper ends 14, preferably so.'substantially all air is excluded. The filled casings l l are then tied to the ring 1 and thus suspended. Theyarealso tied at the bottom t'c the ring 9 to keep the casings? aligned: and to. mainta-in". them under: a slight tension; After: the. casings" lz-l areamounted in the". rack, the: IEllCkflSEDlQGEdliILthB?03/8111 I 1 and; the oven is maintained at the desired temper ture until polymerization is complete. Thereafter, if desired, an after heat treatment may be given at a higher temperature with the tension on the casings l-I somewhat increased to" insure strai'ght'nessof therods formedi Thiszis optionaland may be carried out= inoven: l or'the rack'may be removed to'a second oven maintained at the higher temperature.-

Upon completion of the polymerization there will be obtained in each casing H a rod-of-"polymersubstantially fiawlesssexcept for a few sur face wrinkles about f'to Vgihch'iirdeptli. Fig. III showsase'ction through a*-rod- I5- of polymer withthecasing'l l not-yet rem'ovedi Wrinkles'are indicated at"- IT. The casing H isthen stripped from'the rodwhich isg-roundfi to remove the small wrinkles and given aflawless surface, asection of thefinished ro'dflli being shown-in Fig. IV.

Thefollowing example; wherein all parts are by weight, unless otherwisespecified; illustratesa specific embodiment ofth'e-presentinvention.

Elbampl l A; synthetic: lineaninterpolyamidle was formed:

byreacting 40 parts of hexamethylene diamemonium' adipa'te; 30 parts of; hexaanethyleneidie ammoniumxsebao'ate; and .3oipa-rts of: caprolactama under" conditions; similar torthose recited in .Exe ample I: of Brubaker U.'. 8:. Patent." 2,285,009: lvfolding: powder. produced. from; thezresultlng int-- tenp'olymerrwas extrudedt to formztubular" casings off various wall thicknesses and: diameters: Five: tubular: casings havingspecificationsi indicated irn TableI wereextrudect. Alscrindicatediir'lablel'i 3116313118? diameters of the: finished rods'rcast' in a".

, tion from a rack as in Figs. I andiII'.

The polyamide casings were cut to lengths of inches. A smooth knot was tied at one end of each casing'by creasing the end into about A" flat folds, then. forming a1 loop. and: drawing it tight;

Monomeric methyl methacrylate containing about 0.0015% of alpha,alpha'-azobis (alpha,- gamma dimethylvaleronitrile) by weight of the methyl metliacrylate was heated in a vessel at about. 80?"C..until a syrup having a viscosity of from 15-20 poises was formed. The syrup was divided? into? five portions to which were added further-1 quantities of catalysts as set forth in Table-I; the percentages given being by weight of the. methylmethacrylate. The five polyamide casings were then filled with the five portions of syrup; Each casing was filled to a level so that the finished rod wouldj be about 54 inches in length; Upon filling, the; top: of each; casing; was closed by. tying. a string around. thecasingatathe: liquid level. This same string,-wasusedztossuse pendzeach .ofthe filled.casingssin-a.verticalzposie Arslight? amount of" tension-was maintained onsthe casings by tyingzthe-lower endsthereof td-thevbottomzofi the-rack.

Therack. from. which: the loaded. casings were. suspended was lowered;intozan oven:.whichawast maintainedat about 46 01- by; circulatingchotvairs.

After. about14'8 hours, the rods were. checked to: make surethat the polymerwas firm-r andathat." shrinkage-had taken place; The: rack-1 was: them removed from. the oven! and-placedinza secondi circulatingair oven-.at-aboutl'm" C. for aboutr'i hours. After this time, moreJtensioniwas-aput on: the casings to insure r straightriessof; the. rods;

Each of: the polymethyl. methacrylatevrods;was; stripped. of: its polyamide: casing: and thereafter? each was; ground to the: corresponding finished diameter indicated inthe above; table. Aften grinding; therods werezpolished.tcnform finished; rods: having smoothisuriaces andlhighclar-itya Although the surf aceszcf' the r. polymerizedarods prior to grinding are ver-y 'slightly. irregular, at; the most? only" oneor: two ridges. or. wrinkles: are for-med; these extending? along? the length: of the: rod. In; general, any wrinkles formed: vary from; about: 1% to: in: depth; which; results: in: a: minimum loss of" polymer: inzt'hes. grinding: opera, tion; This illustrates. anlimportant.advantage-of using a polyamide casing which: shrinks substan. tially' uniformly with the polymer: because of its superior elasticity as compared with other types; of" films.

The aboveexample is merely illustrative andz the invention broadly comprises" polymerizing aliquidpolymerizable organic" compound in an:

, elongated cylindricalcasingof a syntheticlinear' casing: having the: indicated. specifications; and

the: amount of: catalysts added; thei methyl. methacrylate syrup prior to introduction inter-the":

, tubular casings.

polyamide ofthe type hereinbefore described:

In-general; a satisfactory casing material mus't possess suitable strength to contain an amount of polymerizable liquid equivalent; to that" necessary a w to cast the maximum size rod desired without bulging, tearing or excessivestretching. In addition to adequate strength or toughness required tocontain a particular amount of a liquid pol'y merizable organic compound; ca sings suitable for 1 use in this invention must alsobe inert to the monomer being polymerized inaddition-to. all additives contained" in the -monomer.. Furthermore, the casing must be nonpermeable to all liquid monomers and; of great importance; the casing material must be sufii'ciently elastic to contract uniformly with-the shrinkage always accompany-- mg the conversion of a liuuid'polymeri'zable com--- pound to a solid polymer. The casing material must not only possess the foregoing properties at ordinary temperatures but should also retain these properties under all polymerization conditions. Obviously, if polymerization is to be carried out with actinic light, the casing should be capable of transmitting actinic light to the contents thereof.

It has been found that synthetic linear polyamides possess the unique combination of properties discussed above to a remarkable degree and thus are outstandingly useful as the material for flexible casing for polymerizing polymerizable liquids in the form of rods. In so far as appli: cant is aware, no other material suitable enough to be practical for this purpose has been found, each plausible material being seriously deficient in one respect or another. For example, cellophane which might appear suitable for the purpose, is not sufficiently elastic to contract uniformly with shrinkage of the polymer and, consequently, deep Wrinkles are formed on the surface of the rod of polymer, requiring much more grinding to give a smooth surface and thus appreciably lowering the yield of finished rod.

While synthetic linear polyamides are in "general suitable for use in the casings of this invention, there are certain qualifying factors which must be observed in order to practice the invention. The thickness of the wall of the casing for practical purposes should be between 0.002 and 0.010 inch. It has been found that, within this thickness range, the thickness of the wall must be correlated-with the particular polyamide selected so that the casing wall as a tensile strength equal to that expressed by the formula PDF as otherwise the casing will tend to tear, bulge or stretch excessively or will not have sufficient elasticity to shrink with the contraction'ofthe polymerizing compound. In this formula P is the maximum pressure, expressed in pounds per square inch, exerted by the polymerizable compound against the Wall of the casing. This maximum pressure is exerted against the wall of the casing at the bottom and is equal to the height of the column of the polymerizable compound in the casing multiplied by the density of the polymerizable compound and, hence, is readily determined. D and T are, respectively, the inside diameter and wall thickness of the casing both expressed in inches and readily measured.

In the above formula F is a factor ranging from 3.5 to 5. Experimental work has shown that if the tensile strength of the casing wall equals PDF 2T where F is any value from 3.5 to 5, the polyamide casing will be satisfactory both with respect tov elasticity and to resistance to tearing or stretching excessively. This formula, except for the factor F, denotes what is known as the hoop stress exerted by a liquid on a cylindrical container as explained on p. 258 in Formulas for Stress and Strain by R. J. Roark, 2nd Ed., 1943, published by McGraw-Hill Company, New York.

Tensile strength as referred to herein is equivalent to yield strength as defined in ASTM Standards on Plastics, September 1948, page 586.

Yield strength is defined as the stress at which a material exhibits a specified limiting permanent set. The tensile or yield strength of the synthetic linear polyamides of the present invention can be measured with any suitable film testing machine of the constant rate of loading type. It should be equipped with a device for recording the tensile load carried by the specimen and recording the rate of jaw separation during the test. Further details of measuring the tensile strength of a plastic film are given in ASTM Standards on Plastics, pages 4'76 to 480. It is measured in a direction perpendicular to the longitudinal axis of the polyamide tubular casing, and the stress in this direction is the abovementioned hoop stress. The tensile or yield strength as used herein is that at 1% Offset. The Offset Method is discussed on pages 586 and 587 of ASTM Standards on Plastics. The tensile strength at 1% Offset indicates that at a stress of X pounds per square inch the approximate permanent set of the material reached the value of 1% (equivalent to .01 inch per inch gage length). As thus measured, the tensile strength of the polyamide film used in Example I was approximately 2,200 pounds per square inch.

The polyamide casings of the present invention may be fabricated by heat sealing films or by directly extruding a molding powder. The latter method is preferred for fabricatin casings in the form of tubes for use in this invention, and may be carried out as follows:

The polyamide molding powder, 'pre-dried to eliminate excess moisture, is fed to the hopper ofa plastics extrusion machine having a tubing die of dimensions for producing tubing having a wall thickness of approximately 0.125 inch. The tubing die is provided with an opening in the center so that a metered amount of air is injected into the extruded tube to maintain the tube in an inflated condition during subsequent handling. The extruded tube, upon emerging from the die maintained at about 200 0., passes through a seriesof coolin .jets, and thereafter the inflated tube is contacted by a variable speed belt, which applies tension to the tube to draw it to the desired final wall thickness. Although the tube has passed through the series of cooling jets whereby it is cooled sufliciently to permit handling, before it contacts the variable speed belt, actually the tension applied to the tube by the variable speed belt causes the tube to be drawn in the so-called hot zone immediately adjacent to the tubing die and preceding the cooling jets. This is a hot drawing operation which does not serve to orient the molecules of the polyamide in the tube as would occur if the tube were cold drawn.

Subsequent to drawing in the hot zone, the tubing is cooled as it passes through the series of cooling jets spaced uniformly around the periphery of the tubing for a distance of approximately one foot longitudinally of the tubing. These jets are constructed to direct uniform streams of air having equalized pressure over the entire outside surface of the tube. The jets provide for a low velocity but a high volume of air, the jets bein directed at an angle against the tubes so that the air moves concurrently with the tube. Upon emerging from the cooling zone, the tube is at a temperature of approximately C. From this point until the tube reaches the variable speed belt, the tube is floated over a series of wooden spools. These spools minimize friction of the tube which, is still sticky at this pointThe type of belt arrangement used to apply ensiunntogthewtube may-vary. Forrexamplei two h rizpntallyrdisposed. parallel belts. may be used to.-contacttheupperand lower-surfaces of. the tube,- the, degree of contactv being .suiiicient to draw. the tube; to thedesiredwallthickness, .but regulated to-- prevent excessive pressureon; the inflated tube. Anothermethodof applyingtene sion-.to,the, tube istoclamp the walls of the tubing together at various intervals, assuming; that the tubing is to. be severedat these intervals,. and tensionzissapplied to the clamping:deviceto-carry out the drawing operation. Following the-drawing;step,- the tube is collapsed at various-intervals and: severed frOm= theadjacent portion. at the collapsed section.

Tubing; having a. particular wall. thickness. is readily..- obtainedgbyvarying, the tension applied to;theex truded,-tube through regulating the speed of thervariablejspeed. belt.- Thehot tubin may be. drawn froma wallthickness. ofabout. 25 inch. downtapractically any desired. thickness, for: example, from 0.00025- inch to. 0.005 inch. The aboyemethod. provides for the continuous production of thin, wall. polyamide tubing. having reproducible diameter and. Wall. thickness, and iteliminates dragging of, the, hot tubin at the die,-v exit as,is, customarily obtained. when. directly extruding thin wall tubing.

Casingsifabrioated, from, any type of; synthetic linear, polyamide; or interpolyamide. disclosed in Carothers U. S. Patent.-2;130.,523.may be usedin the present. invention. It is,pr eferr.ed, however,

toruse; casings fabricated from the typeof. inter.-

polymer illustrated. in.Example- I. Besidesthe interpolymer'given. in. Example I, another particularly Preferred, interpolymer is .f ormed.-,by re.- acting 36 parts of hexamethylene diammonium adipate, 26, parts of. hexamethylenediamnionium sebacate, ,and. 38: parts of caprolactam.

The manner. of handlingthepolyamide casings of. this inventionwith regard to. sealing. filling with liquid. monomer, suspending the. filled. case ings; during the polymerization. cycle, carrying out polymerization,- and finally stripping the polyamide films from. the polymer, form will. be .i

acrylamide, methylacrylate, methyl, chloroaor'y-late, methyl methacrylate, ethyl methacrylate, butyl methacrylate, ethoxyethyl, methacrylate, glycol dimethacrylates, methyl ethacrylate, ethyl ethacrylate, acrylonitrile, methacrylonitrile; other vinyl and vinylidene compounds, e. g., vinyl acetate,- vinyl chloride, vinylidene chloride; vinyl ethers, styrene, methyl styrene, allyl. chloride, and dimethyl itaconate. Numerous other organic compoundspossessing. the requisite properties herein discussedwill. readily occur to those skilled in theart.

It. is. ordinarily preferable. to start with the polymerizable liquid organic compound. in par.- tially. polymerized condition, 1. e., as a. more or less, viscous syrup rather than with a, straight organic-liquid. The use ofasyru shortensthe duration of. they process, and also reduces, the possibility of any leaks throughthe-sealedportions of the casing. Usually asyrup, having a viscosity of between 10 and20 poises is preferred, butitis tobe understoodthat the present. invention is not limited to the use of a liquid polymerizable organic compound of any Particular consistency, the monomeric form being entirely satisfactory and syrups of higher viscosity. being advantageous under certain, conditions. Furthermore, various dyestuffs, plasticizers, lubri: cants, pearlescent materials, other types of eifect materials, and other modifiers may be incorthe preferred catalysts are alpha,alpha-az obis readily apparent-to thoseskilledinthe art,. As

illustrated. in. Example I, the most. expedient methodof handling thefilled. casingsduring. the polymerization, cycle is to. suspend the: casing from. one end and fix: the. other. extremity. to. a rigid; supportwith applicationi of. a, slight, amount of. tension on. the mold. Variousprecautions to be taken. will. also, occur. in: handling. the r casings prior. to filling and during. polymerization. For example, excessive stretching of the casing-should be. avoided. when, sealing either. extremity, thereof by tying a knot. Other means for sealing, the extremities, of the casing may be used.

'llheinvention. is manifestly applicable broadly to. liquid, organic compounds that. may be poly.-

merized to, polymers solid atordinary temperae tunes, Obviously, the. invention. is. of greater valueas applied. to those compounds .which, give solid polymers. of the-most useful properties. and,

'normallythe invention will. be-applied to polymerizable, organic. compounds which giverigid (alpha,gamma dimethylvaleronitrile) alpha,alpha' -azo-diisobutyronitrile; diethyl alphaalphaf azodiisobutyrate; and. alpha,alpha'-azodicyclo hexanecarbonitrile.

When polymerization is to be carried'outwith actinic, light, various polymerization. catalysts which may be used include benzoin and, similar vicinalketaldonyl and acyloin compounds asdisclosed in Agre U. S. Patents. 2,367,660. and 2,367,661, and also various azo-type catalysts such as alpha,alpha-azodiisobutyronitrile, as disclosed in Salisbury U.. S. application. Serial Number 655,013 now abandoned.

Depending'upon the particular conditions, the amount; of catalyst and the liquid, polymerizable organic compounds, the temperature of polymer: ization may vary fromroom temperature up to C. When photopol'yinerization is used, temperatures below room temperature may be advantageous, particularly. when. large diameter castingsare-being polymerized. The selection. of an optimum temperature under any givencond-ition as Well .as the. specific-catalyst and amount thereof used, will .be'basedon the usual considerations-of the-prior art, and-will no1-,beappreciably influenced by-anyspecific considerationrela-ting to'the instant invention.

Anadvantage of the; present invent-ionis that it. provides, a. simplified. and more economical process of; producing polymeric: materials in. the form of, elongated shapes ascompared, withiprevailing; prior art procedures. A more specific 9 advantage is that it provides a process of preparing methyl methacrylate ,rods in yields substantially greater than in prevailing prior art processes.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in' the appended claims.

The invention claimed is:

1. In a process of polymerizing a liquid polymerizable organic compound in the form of a rod, the steps comprising introducing said polymerizable compound into a vertically positioned, elongated cylindrical casing of a substantially unoriented synthetic linear polyamide closed at the bottom, the wall of said casing being 0.002 to 0.010 inch thick and having a tensile strength equal to PDF wherein P is the maximum pressure expressed in pounds per square inch, exerted by said polymerizable compound against the wall of said casing, D is the inside diameter, expressed in inches, of said casing, F is a factor ranging from 3.5 to 5, and T is the wall thickness of said casing expressed in inches, closing the upper end of said casing, and thereafter polymerizing said polymerizable compound contained in said casing while maintaining said casing in vertical position in a gaseous medium.

2. Process as set forth in claim 1 wherein said casing is 12 to 72 inches long and has an inside diameter of 1 to 6 inches.

3. Process as set forth in claim 1 wherein said casing is 12 to 54 inches long and has an inside diameter of 1 to 2 inches.

4. Process as set forth in claim 1 wherein said liquid polymerizable organic compound is methyl methacrylate.

5. Process as set forth in claim 2 wherein said liquid polymerizable organic compound is methyl methacrylate.

6. Process as set forth in claim 3 wherein said liquid polymerizable organic compound is methyl methacrylate.

JOHN BOYKO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,307,817 Austin Jan. 12, 1943 2,485,798 Whyte et a1. Oct. 25, 1949

Claims

1. IN A PROCESS OF POLYMERIZING A LIQUID POLYMERIZABLE ORGANIC COMPOUND IN THE FORM OF A ROD, THE STEPS COMPRISING INTRODUCING SAID POLYMERIZABLE COMPOUND INTO A VERTICALLY POSITIONED, ELONGATED CYLINDRICAL CASING OF A SUBSTANTIALLY UNORIENTED SYNTHETIC LINEAR POLYAMIKDE CLOSED AT